At the age of 13 is it normal to have menstruation 2 times a month or you should be worried.

It's often normal during the teen years to have irregular periods. When a girl's period is irregular, it might come more than once a month or only come every few months. Some girls find they get their period more than once some months, then they might not have another for several months.

Explanation:

the electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, x-rays, and gamma-rays.

not only is it colder, it also becomes darker, less salty, and more dense.